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Chapter 8: Friction

Chapter 8: Friction. Example 8.6. Determine the normal force P that must be exerted on the rack to begin pushing the 100kg pipe up the 20° incline. The coefficients of static friction at points of contact are ( μ s )A = 0.15 and ( μ s )B = 0.4. Example 8.6. P. N 2. y. x. N 1. P. F B.

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Chapter 8: Friction

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  1. Chapter 8: Friction

  2. Example 8.6 Determine the normal force P that must be exerted on the rack to begin pushing the 100kg pipe up the 20° incline. The coefficients of static friction at points of contact are (μs)A = 0.15 and (μs)B = 0.4.

  3. Example 8.6 P N2 y x N1 P FB

  4. Example 8.7 The uniform stone has a mass of 500kg and is held in place in the horizontal position using a wedge at B. if the coefficient of static friction μs = 0.3, at the surfaces of contact, determine the minimum force P needed to remove the wedge. Is the wedge self-locking? Assume that the stone does not slip at A.

  5. Example 8.7 4905N 0.5m 0.5m 0.3NB FA 7° NB NA 7° Since P is positive, the wedge must be pulled out. If P is zero, the wedge would remain in place (self-locking).

  6. Example 8.8 The turnbuckle has a square thread with a mean radius of 5mm and a lead of 2mm. If the coefficient of static friction between the screw and the turnbuckle is μs = 0.25, determine the moment M that must be applied to draw the end screws closer together. Is the turnbuckle self-locking?

  7. Example 8.8 2 kN M 2 kN

  8. Example 8.9 The maximum tension that can be developed In the cord is 500N. If the pulley at A is free to rotate and the coefficient of static friction at fixed drums B and C is μs = 0.25, determine the largest mass of cylinder that can be lifted by the cord. Assume that the force F applied at the end of the cord is directed vertically downward.

  9. Example 8.9 Impending Motion Impending Motion 135° B C T1 500N 135° 277.4N W = mg

  10. Example 8.10 The uniform bar has a total mass m. If it is assumed that the normal pressure acting at the contracting surface varies linearly along the length of the bar, determine the couple moment M required to rotate the bar. Assume that the bar’s width a is negligible in comparison to its length l. the coefficient of static friction is equal to μs.

  11. Example 8.10 z M W dF dN y x dF dN

  12. Example 8.11 The 100mm diameter pulley fits loosely on a 10mm diameter shaft for which the coefficient of static friction is μs = 0.4. Determine the minimum tension T in the belt needed to (a) raise the 100kg block and (b) lower the block. Assume that no slipping occurs between the belt and the pulley and neglect the weight of the pulley.

  13. Example 8.11(a) θs rf P1 Impending Motion P2 R 981N T 52 mm 48 mm

  14. Example 8.11(b) θs rf Impending Motion P1 P2 R 981N T 52 mm 48 mm

  15. Example 8.12 A 10kg steel wheel has a radius of 100mm and rest on an inclined plans made of wood. If θ is increased so that the wheel begins to roll down the incline with constant velocity when θ = 1.2°, determine the coefficient of rolling resistance.

  16. Example 8.12 98.1 N 98.1 cos1.2° N 98.1 sin1.2° N 1.2° a N

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